This project is attempting to exploit the rodent olfactory system in studies of neurobehavioral plasticity. The approach is predicated upon (1) the critical importance of olfaction in the lives of vertebrates from fish to primates; (2) the existence of specific animal odors (putatively 'pheromones') upon which the survival of the individual and the species depends in various rodents; (3) the pervasiveness of sensitization and habituation (two experimental 'models' of learning and memory) to olfactory stimuli and to electrical stimulation of the olfactory bulb and (4) some unique morphological and functional features of the rodent olfactory bulb (including its relative symmetry and simplicity, its laminar 'cortical' organization, its segregation of input and output pathways, and its intimate association with limbic brain regions traditionally implicated in mammalian learning and memory. Electrophysiological experiments are being pursued in two converging areas: In studies of the first type, sensitization anf habituation are produced by electrical stimulation of the rodent olfactory bulb. The effects are observed on the activity of single and multiple units. The ultimate objective in this case is to relate observed changes in unit activity to structural changes detectable by subsequent electron-microscopic examination of the stimulated tissue. Studies of the second type are mainly concerned with olfactory unit responses to pheromone-like odors. This work has already led to the important discovery of unit activity patterns related to periodic nasal air flow and is being pursued along three main lines: First, studies of possible centrifugal influences upon the inhalation-related activity of olfactory bulb units; second, a search for inhalation- related patterns of unit activity elsewhere within the rodent olfactory system; and third, the extension of our recently-developed chronic unit recording technique to studies of olfactory system unit responses to pheromone-like odors in alert, behaving, animals.